Polypropylene resins have excellent properties such as molding processability, water resistance, oil resistance, acid resistance, and alkali resistance. The polypropylene resins, however, are disadvantageously inferior in heat resistance, rigidity, and impact resistance and therefore known to be prepared into compositions supplemented with a polyphenylene ether resin. In the compositions, the polypropylene resin forms a matrix phase, and the polyphenylene ether resin forms a dispersed phase. As a result, the resulting resin composition is known to have improved heat resistance and rigidity.
Patent Documents 1 and 2 have each proposed a composition of a polyphenylene ether resin and a polypropylene resin. Also, Patent Documents 1, 3, and 4 have each proposed a composition of a polyphenylene ether resin, a polypropylene resin, and a hydrogenated block copolymer. As disclosed therein, the hydrogenated block copolymer acts as an admixture for the polyphenylene ether resin and the polypropylene resin and is a component that further confers impact resistance.
Referring to the hydrogenated block copolymer used in the inventions described in Patent Documents 1, 3, and 4, these documents make the following statements.
Patent Document 1 describes a hydrogenated block copolymer prepared by hydrogenating a block copolymer consisting of a polymer block A composed mainly of a vinyl aromatic compound and a polymer block B composed mainly of a conjugated diene compound in which the ratio of the amount of vinyl bonds to the amount of all bonds in the conjugated diene compound is 30 to 95%.
Patent Document 3 describes a hydrogenated block copolymer prepared by hydrogenating, at a rate of 65 to less than 80%, a block copolymer consisting of a polymer block A composed mainly of a vinyl aromatic compound and a polymer block B composed mainly of a conjugated diene compound in which the ratio of the amount of vinyl bonds to the amount of all bonds in the conjugated diene compound is 65 to 75%.
Patent Document 4 describes a hydrogenated block copolymer prepared by hydrogenating a block copolymer consisting of a polymer block A composed mainly of styrene and a polymer block B composed mainly of butadiene in which the ratio of the amount of vinyl bonds to the amount of all bonds in the butadiene is 70 to 90%, wherein the amount of bound styrene is 15 to 50% by mass, the hydrogenated block copolymer has a number-average molecular weight of 100000 or smaller, and the polymer block A has a number-average molecular weight of 8000 or larger.